1. Field of the Invention
The present invention relates in general to liquid crystal displays and, more particularly, to a structural improvement in such liquid crystal displays (LCD) for easily controlling both the width of a black matrix and the size of R (red), G (green) and B (blue) filters by forming the black matrix and the R, G and B filters on different substrates. Forming of the R, G and B filters and the black matrix on different substrates also allows a color filter, having relatively lower colorimetric purity and transmissivity, to be formed separately from the other color filters thereby improving the displaying efficiency of the LCD.
2. Description of the Prior Art
FIG. 1 shows a typical liquid crystal display. As shown in the drawing, the typical liquid crystal display (LCD) includes a top glass substrate 1a. Three color filters, that is, R (red), G (green) and B (blue) filters 3R, 3G and 3B, are formed on the bottom surface of the top substrate 1a. Formed between the color filters on the top substrate 1a is a black matrix 2. The above LCD also includes a bottom glass substrate 1b opposite from the top substrate 1a. A plurality of ITO (indium tin oxide) drive electrodes 4 are formed on the top surface of the bottom substrate 1b. The above ITO electrodes 4 are aligned with the R, G and B filters of the top substrate 1a, respectively. After preparing the above top and bottom substrates 1a and 1b, liquid crystal is injected between the two substrates 1a and 1b prior to enveloping the two substrates 1a and 1b. When the ITO electrodes 4 of the above LCD are applied with a voltage, the LCD displays a color picture in accordance with intrinsic characteristics of the liquid crystal interposed between the two substrates 1a and 1b.
FIGS. 2A to 2F show a process for producing the above LCD. As shown in FIG. 2A, a light intercepting chrome layer is deposited on the top glass substrate 1a through either an electron beam deposition or a vacuum deposition. An example of vacuum deposition for forming the chrome layer is sputtering. Deposition of the light intercepting chrome layer is followed by forming of the black matrix 2. The above matrix 2 is formed through application of a photoresist, exposure with a mask, developing, wet etching, etc. Thereafter, a green filter patterning photoresist resin 3 is applied on the black matrix 2 prior to exposing with a mask. The top substrate 1a in turn is dyed with a dye having a given spectrum characteristic thereby forming the green filter 3G as shown in FIG. 2B. Thereafter, a red filter patterning photoresist resin 3 is applied on the resulting substrate 1a of FIG. 2B as shown in FIG. 2C. The substrate 1a in turn is exposed with a mask and dyed with a dye having a given spectrum characteristic thereby forming the red filter 3R as shown in FIG. 2D. A blue filter patterning photoresist resin 3 is applied on the resulting substrate 1a of FIG. 2D as shown in FIG. 2E. The substrate 1a in turn is exposed with a mask and dyed with a dye having a given spectrum characteristic thereby forming the blue filter 3B as shown in FIG. 2F. That is, the R, G and B filters are formed on the top substrate 1a in order of the G filter 3G, R filter 3R and B filter 3B.
In the above process for forming the R, G and B filters on the substrate 1a, the green filter 3G has less bonding force for being bonded to the other colors in comparison with the other filters. Therefore, the green filter has to be primarily formed on the substrate 1a by exposing the substrate 1a with a mask after applying the green filter patterning photoresist resin on the substrate 1a. Thereafter, the red and blue filters are formed on the green filter in the same manner as described for the green filter. In the above process, it is required to carefully check both the exposing light intensity and the development due to a narrow developing margin.
However, as both the R, G and B filters and the black matrix are formed on the same plane, it is very difficult to technically reduce the area of the black matrix on a screen in view of aperture efficiency. Additionally, the G filter has an inferior bonding force for being bonded to the glass substrate because the G filter intrinsically has lower colorimetric purity and transmissivity than the other filters. In this regard, the G filter has to be formed on the glass substrate while either changing the step for forming the G filter with the other steps for forming the other filters or using a specified method.